Airfix 1/48 P-51D 75 gal. Drop Tanks

I recently bought two Airfix 1/48 P-51D Mustang kits.  The article in the September 2017 issue of Airfix Model World showed that the kit offered an excellent cockpit and a correct reproduction of the main wing spar at the rear of the main landing gear bays.  The article also showed that the kit included 75 gallon drop tanks marred by the lack of clinch flanges (page 52).  (The 1/72 Aixfix P-51D kit also suffers from this flaw.)  When Airfix announced that the 1/48 kit was available on their website, the accompanying photos showed 75 gallon tanks with the necessary clinch flanges.  On opening my kits, I was disappointed to find that the tanks provided do not, in fact, have the flanges.  I assembled one and compared it with a 75 gallon tank from a Tamiya P-51D kit and found that the Airfix rendering is much larger.  I then measured other 75 gallon tanks in my collection and stash and discovered that their sizes vary.  The Tamiya, Arii, Hobby Boss and Meng tanks are scale 6'3" long.  Accurate Miniatures (from their P-51B kit) and Eduard's Brassin tank are 6' long.  Airfix's measured 6'6" long.  I then checked some references to determine the correct length for this tank.  Three (Kokufan, Kagero and Aero Detail) had scale drawings showing 6' and two (MMP and AJ Press) showed 7'3".  An internet search provided no information.  Does anyone know the correct dimensions of the 75 gallon drop tank used on the P-51B and D Mustangs?  Can anyone suggest a source for this information?  I was thinking of contacting the Air Force Museum and the Cavanaugh Flight Museum.  It is worth noting  that I found evidence that there was a larger capacity metal tank with the same configuration as the 75 gallon tank that also seems to have been used on Mustangs.  Any suggestions or information would be appreciated.  No rush.  Thank you in advance.